A comprehensive model for photon noise and correlations in semiconductor cascade lasers is presented. Photon emission events in different gain sections of cascade lasers are correlated. These correlations are found to be positive and arise because the gain sections are connected electrically. The scaling of photon correlations and intensity noise with the number of cascade sections is discussed. The model presented in this letter is applicable to a variety of cascade laser structures including bipolar interband cascade lasers and unipolar intersubband cascade lasers. For comparison, photon noise and correlations in parallel lasers arrays are also discussed.

We report on a poling process of soda-lime glasses that reduces their surface conductivity by five orders of magnitude. We show that this process enables the in-plane poling of high (180 °C) electro-optic (EO) polymers coated on ion-exchanged channel waveguides fabricated in soda-lime glasses for hybridmodulators.

We report a simple fabrication process for realizing waveguides on periodically poled lithium niobate which preserves both the nonlinearity and the domain inversion. This so-called soft proton exchange has been used to generate highly efficient optical parametric fluorescence in the 1.48–2.01 μm region using a pump around 830 nm. The measured normalized efficiency is 130% for an effective interaction length of 1.3 cm. This experimental figure is very close to the maximum theoretically predicted value of 140%

Single-mode tunable quantum-cascade distributed feedback lasers emitting at 4.6–4.7 μm wavelength are reported. The lasers employ strained heterostructurematerial with global strain compensation to provide the large band offset needed for high-performance short wavelength operation. Pulsed, continuously tunable single-mode emission is achieved from 90 to 300 K with a tuning range of 65 nm. Peak output power levels of 100 mW at room temperature are obtained. In continuous-wave operation, current tunable single-mode emission is demonstrated around liquid-nitrogen temperature with a tuning range of 20 nm (over a current range of 450 mA). The maximum output power in continuous wave at 80 K is 150 mW.

We report bistable switching of the output direction in certain triangular diodering lasers. These lasers operate unidirectionally at large drive currents, with up to 98% of the output power emerging from either the clockwise or the counterclockwise direction. The preferred direction can switch back and forth, with a large hysteresis loop, as the drive current is varied. Up to 20 mW of optical power changes direction at each switch. We propose an explanation based on the theory of two-mode competition via gain saturation.

High-temperature dependence, up to 150 °C, of the photoresponsivity of ZnS, ZnSTe, and ZnSSe photodiodes was investigated in this study. It was found that, in general, the responsivity at higher temperatures will shift to longer wavelengths because of band-gap narrowing. A remarkable observation is that the near-band-edge responsivities of these diodes increase at higher temperature. We believe that this observation is attributed to the change of the density-of-state distribution due to lattice expansion at high temperatures, and a simplified model is used to illustrate this hypothesis.

The growth of the layered chalcogenide GaSe on cleaved GaAs(110) surfaces was investigated with photoemission and low-energy electron diffraction(LEED). GaSe filmsgrow with their c axis perpendicular to the GaAs(110) surface.LEED patterns after initial film growth are a superposition of rectangular GaAs:Se spots and two hexagonal domains rotated by with respect to the GaAs axis. At higher film thickness a hexagonal LEED pattern with GaSe 〈120〉 ‖ GaAs 〈001〉 is obtained.

We have studied the influence of InP buffer-layer morphology in the formation of InAsnanostructuresgrown on InP(001) substrates by solid-source molecular-beam epitaxy. Our results demonstrate that when InPbuffer layers are grown by atomic-layer molecular-beam epitaxy,InAsquantum dot-like structures are formed, whereas InPbuffer layersgrown by MBE produce quantum-wire-like structures. The optical properties of these corrugated structures make them potential candidates for their use in light-emitting devices at 1.55 μm.

It is demonstrated here that nonresonant Raman spectroscopy can be used for unequivocal determination of short-range order in ultrathin films, using different structures of titanium dioxide as the model system. Titania films as thin as 7 nm sputter deposited on 〈111〉 Si have been analyzed and their phase content determined.

Cleaved MgO(100) single crystals were implanted with 30 keV ions with doses varying from to and subsequently thermally annealed from 100 to 1100 °C. Transmission electron microscopy observations revealed the existence of sharply rectangular nanosize voids at a depth slightly shallower than the helium-implantation range. Monitoring of the defect depth profile and the retained amount of helium was performed by positron-beam analysis and neutron depth profiling, respectively.

Surface and subsurface structures of porous GaN prepared by anodizing epitaxialGaN layers grown on SiC substrates are investigated by atomic-force microscopy. Comparison of the images of the porous GaNsurfaces with those taken on planes cleft perpendicular to the surface shows that the pores are formed along the boundaries of columnar structures of the original GaNfilms. X-ray investigations show that the porous GaN has less residual stresses than the initial GaNepitaxial layers. Use of porous GaN as a buffer layer for growth of low-stress GaN is proposed.

Gallium arsenide(GaAs)nanowires have been synthesized in bulk quantities and high purity by laser-assisted catalyticgrowth.Field-emissionscanning electron microscopy and transmission electron microscopy investigations show that the GaAsnanowires are produced in >90% yield, are single crystals with 〈111〉 growth axes, and have diameters varying from three to tens of nanometers, and lengths extending to tens of micrometers. Photoluminescence (PL) measurements made on individual GaAsnanowires show large blueshifts in the PL peak position compared to bulk GaAs, and are consistent with strong quantum confinement. The implications of these results are discussed.

Hydrogen-etched 6H SiC (0001) surfaces have been studied by reflection high-energy positron diffraction and atomic force microscopy. It was found that residual damage on the surfaces were effectively removed by the hydrogen etching as compared to the HF etching after the oxidation. The hydrogen-etched surfaces were atomically flat. After the oxidation following the hydrogen etching, the surface roughness was found to increase and an anomalous dip structure appeared in the rocking curve of the reflection high-energy positron diffraction.

Photothermal spectroscopy is demonstrated using a high-aspect-ratio multilayer cantilever to measure adsorbed dimethyl methylphosphonate, which has an optical absorbance of in the near infrared range. Detection sensitivity was 160 pW for a reed of 6 mm in length, 2 mm in width, and 10 μm. Sensitivity of the cantilever is compared to a thermal diffusionmodel that accounts for conduction loss through the cantilever clamp and to air along the length of the cantilever surface.

Growth of single-crystalgraphite free-standing plates has been achieved by a microwavehydrogen-plasma etching of graphitepowder and nickel mesh. The plates resemble a knife blade and grow in the direction with long crystals exceeding 100 μm. Hexagonal growth features at the edges and electron diffraction patterns confirm the single-crystal nature of these ultrathin plates. Electron microprobe and Raman spectroscopy indicate the presence of graphite.Diamond crystals nucleate on these plates and they grow simultaneously. We suggest that the paradoxical growth of graphite in a hydrogen plasma, under conditions in which graphite is usually etched away, is possible because of a protective coating by a Ni–C–H phase. This thin coating allows for transport of carbon atoms from the gas phase to the growinggraphite surface.

We have templated Cu(100) surfaces with self-assembled arrays of atomic nitrogen islands and then used these islands as masks for Co growth. This method of nanolithography enables the creation of Co dot arrays with dot densities Adjusting the nitrogen coverage also enabled the creation of arrays of Co lines spaced 10 nm (0.01 μm) apart.

We report a photoluminescence study of high-purity layers grown by molecular-beam epitaxy over the composition range. The intense excitonic line dominates in the photoluminescence spectra of the layers. The full width at half maximum of the excitonic line is in excellent agreement with values calculated by Lee and Bajaj [J. Appl. Phys. 73, 1788 (1993)] for perfectly random alloys, and in the spectra of the layers with AlAs fractions of and it equals to 1.24 and 1.48 meV, respectively. A linear dependence of the exciton line intensity on excitation power evidences negligible concentration of nonradiative recombination centers in the layers.

We describe a detailed device fabrication technique for the formation of a lateral quantum dot using a multilayered gated design. In our versatile system, a quantum dot is electrostatically defined by a split gate and two overlaying finger gates which introduce entrance and exit barriers to the dot. Periodic and continuous conductance oscillations arising from Coulomb charging effects are clearly observed in the transport properties at low temperatures.

We present experimental techniques to analyze the electroluminescence(EL) of polymer light-emitting diodes following the removal of an applied voltage pulse. We explain the fast modulation of the EL intensity at turn-off in terms of the sudden reduction of the Langevin recombination rate, and extract the time evolution the device’s internal electric field at the recombination zone during the application of a voltage pulse. The results are compared to, and found to be consistent with, those of simple numerical modeling. The subsequent long-lived EL tail is analyzed to give the time evolution of the carrier distributions at the recombination zone once the voltage pulse has been removed.

We have investigated the energy loss rate of hot holes as a function of carrier temperature in p-type inverted modulation-doped (MD) Si/SiGe heterostructures over the carrier sheet density range at lattice temperatures of 0.34 and 1.8 K. It is found that the energy loss rate (ELR) depends significantly upon the carrier sheet density, Such an dependence of ELR has not been observed previously in p-type SiGe MD structures. The extracted effective mass decreases as increases, which is in agreement with recent measurements on a gated inverted sample. It is shown that the energy relaxation of the two-dimensional hole gases is dominated by unscreened acoustic phononscattering and a deformation potential of is deduced.